HP 54645A User's And Service Manual page 111

MegaZoom Concepts
Changing the time reference position
Post Acquisition Processing
In addition to changing display parameters after the acquisition, all of the
measurements and math functions can be done after the acquisition. The
measurement and math functions will be re-calculated as you pan/zoom and
turn on/off channels.
As you zoom in and out on the signal, you affect the resolution of the display,
and the resolution of functions and measurements. For example, if you do an
FFT on a channel, it is done on the points on the screen. As you pan through
the waveform (change the delay), you can look at the spectrum as a function
of time. As you zoom in on the signal, the effective sample rate increases and
the frequency span increases (the resolution decreases). As you zoom out,
the effective sample rate decreases, and the frequency span decreases (the
resolution increases).
One of the benefits of the HP 54645A/D is that you can change display modes
after you acquire data. You can turn vectors on/off, or switch from peak
detect to normal display modes. If you acquire data in normal mode, then
switch to peak detect, you will see all the peaks in memory. You are not
guaranteed to see every 5-ns peak.
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